docs: def build_multi_mfd(mfd):
      """
      Parses the MultiMFD as a Node
  
      :param mfd:
          MFD as instance of :class:
          `openquake.hazardlib.mfd.multi_mfd.MultiMFD`
      :returns:
          Instance of :class:`openquake.baselib.node.Node`
      """
      node = Node("multiMFD", dict(kind=mfd.kind, size=mfd.size))
      for name in sorted(mfd.kwargs):
          values = mfd.kwargs[name]
          if name in ('magnitudes', 'occurRates'):
              if len(values[0]) > 1:  # tested in multipoint_test.py
                  values = list(numpy.concatenate(values))
              else:
                  values = sum(values, [])
          node.append(Node(name, text=values))
      if 'occurRates' in mfd.kwargs:
          lengths = [len(rates) for rates in mfd.kwargs['occurRates']]
          node.append(Node('lengths', text=lengths))
      return node